"That was the first time she ever saw the water," the girls' mother, Nicole Rutherford, of Bethany Beach, Del., told ABCNews.com. "We were just cooking up hot dogs and having a good time because the weather was so nice. She was staring out at the water almost in a trance."

After Rutherford took the picture of Sierra clenching her fists and making her "fierce face" towards the water, Rutherford posted the picture on her Facebook page, which elicited comments from friends saying that she looked like Tim Tebow doing his famous "Tebow" pose.

"Sierra is going to be our sports girl," Rutherford said. "She is so tall for her age. Her dad wants her to be the volleyball or basketball player of the family."

The picture caught the eye of family friend, Chris Chamblee, who posted the picture on Reddit last week, causing it to quickly trend on the site with more than 929,500 views.